It is common in the mining field to transport material through the bore panel of a mine on a flexible continuous tram (FCT). FIGS. 1 and 2 illustrate a known FCT. The mined material is transported by a continuous transport belt that runs on rollers supported on column supports above transverse beam structures. The beam structures and column supports are components of cars that are coupled together to form a train, which may be as much as 550 feet long. Each car includes guides for an endless crawler chain that is driven by sprockets associated with drive cars of the tram and carries transverse crawler pads that enable the entire tram to be moved periodically as the mining progresses. Commonly, the tram is moved every three days or so.
The tram is assembled in sections of, say, 60 feet in length, each section consisting of numerous standard cars, a drive car at each end and a takeup car that enables the length of the section to be adjusted in order to maintain a desired tension in the chain. The takeup car consists of a center beam structure on which a segment of the transport belt is supported and a side beam structure on either side of the center beam structure that is connected to the center beam structure by large bolts. Adjustment of the takeup car is accomplished manually by loosening the bolts, setting the desired chain tension using portable hydraulic jacks inserted between the two side beam structures on each end of the car, inserting shims between one or both side beam structures and the center beam structure and tightening the nuts on the bolts that join the beam structures. Once the tension has been set by adjusting the take-up car, the actual tension in the chain can vary significantly due to changes in the relative positions of the cars, such as negotiating a turn in the mine panel.
The tension in the crawler chain is very critical. If the chain is allowed to run too loose, the rate of wear of the chain guides of the drive units (which are highly subject to wear in all events) is greatly increased. If the chain is too tight, the chain guides of the drive unit are very prone to braking. Each time that a chain guide of a drive unit has to be changed because of wear or breakage, the FCT to be taken out of operation to replace the guide, which requires three mechanics working for up to twelve hours to make the repair. Running the tram with the crawler chains too loose can also result in chain links becoming balled up in a guide somewhere and in breaking of the chain. Replacing a broken chain can take as much as 24 hours. The costs of running an FCT with improper tension in the while the repairs are made, is, obviously, considerable.